1. Field of the Invention
The present invention relates generally to a coating method and apparatus, and more particularly to a curtain-coating method and apparatus for coating a continuous web with liquid compositions in the manufacture of photographic film, photographic printing paper, magnetic recording tapes, adhesive tapes, pressure-sensitive recording paper, offset printing plates, and so forth.
2. Description of Related Art
In curtain coating, a traveling web or object is coated by a free-falling curtain of coating liquid that is caused to impinge onto the traveling web or object to form a layer thereon. The curtain coating apparatus is widely used for the manufacture of photographic film, etc., which require a uniform coating.
If the web travels at a high speed, the free-falling curtain is disturbed by an air carried along by the traveling web. This causes the web to be unevenly coated. To solve this problem, there has been proposed a variety of coating apparatuses with air shielding means: a coating apparatus in which a plurality of curried air shields are attached to a coating head (U.S. Pat. No. 3,867,901); a coating apparatus in which a vacuum chamber is arranged close to a web on a backup roller (Japanese Patent No. 2,767,712); a coating apparatus in which an air shield member having a plane parallel to a web is arranged close to the web (Japanese Patent Provisional Publication No. 3-123658); a coating apparatus provided with a means for jetting air in opposition to the air carried along by the traveling web (Japanese Patent Provisional Publication No. 3-65266); and a coating apparatus that blocks the air carried along by the traveling web by arranging an elongated brush extending across the web (U.S. Pat. No. 5,181,963).
The air shielding means of these conventional coating apparatuses must be arranged as close as possible to an impingement position where the free-falling curtain impinges onto the web. That is because the airflow cannot be effectively blocked if the air shielding means is located away from the impingement position.
However, if the air shielding means is arranged close to the impingement position in the conventional coating apparatuses, the air shielding means is contaminated with the coating liquids due to splashes of the coating liquids when a curtain deflector moves at the start of the coating. Consequently, the coating liquids that adhere to the air shielding means drop onto the web during the coating and cause the uneven coating.
To solve this problem, in the coating apparatus of U.S. Pat. No. 5,338,359, a preparation pan is positioned beneath the hopper lip during hopper preparation wherein flow within the hopper is chaotic and the curtain is not stable. The preparation pan includes edge walls spaced apart from the edge guides to stabilize the unsteady curtain within the preparation pan. The coating apparatus minimizes splashing and splattering of the coating liquids thereby minimizing contamination of the coating equipment.
In the coating apparatus of U.S. Pat. No. 5,338,359, however, an elevator for moving up and down the preparation pan works incorrectly since the elevator is contaminated with the coating liquids. Moreover, it is impossible to move the preparation pan with a large capacity within a limited space. Thus, it is necessary to use a small-sized preparation pan and discharge the coating liquids collected in the preparation pan.
In view of the foregoing, it is an object of the present invention to provide a coating method and apparatus that prevents an air shielding device from being contaminated with coating liquids due to splashes of a free-falling curtain, and the like.
To achieve the above-mentioned object, the present invention is directed to a coating method, comprising the steps of: causing a curtain of a coating liquid to free-fall from a coating head; starting to coat a traveling web with the coating liquid by causing the curtain of the coating liquid to impinge onto the traveling web; and moving, just after the starting step, an air shielding device close to an impingement position where the curtain of the coating liquid impinges onto the traveling web so as to shield the curtain of the coating liquid from an air carried along by the traveling web, the air shielding device being withdrawn from the impingement position before and at the starting step.
To achieve the above-mentioned object, the present invention is also directed to a coating apparatus, comprising: a coating head from which a curtain of a coating liquid free-falls, the curtain of the coating liquid impinging onto a traveling web to coat the traveling web with the coating liquid; an air shielding device for shielding the curtain of the coating liquid from an air carried along by the traveling web; and a moving device for moving, just after a start of coating, the air shielding device close to an impingement position where the curtain of the coating liquid impinges onto the traveling web, the air shielding device being withdrawn from the impingement position before and at said start of coating.
According to the present invention, the coating apparatus has the moving device for moving the air shielding device close to the impingement position where the free-falling curtain impinges onto the web, just after the start of coating. This prevents the air shielding device from being contaminated with splashes of the coating liquids, and the like.